Propellant grain

ABSTRACT

A propellant grain is wrapped with glass fiber tape and fitted with epoxy end pieces to inhibit burning in those areas. A fluorocarbon grain is etched with hydrochloric acid and then immersed in lacquer before being wrapped.

United States Patent Carpenter et a1.

[ Oct. 24, 1972 154] PROPELLANT GRAIN [72] Inventors: David W. Carpenter; Charley R.

Rodgers, both of China Lake, Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy [22] Filed: May 4, 1070 [21] Appl. No.: 34,032

[52] US. Cl. ..264/3, 102/ 103, 149/5 [51] Int. Cl. ..C06h 21/02 [58] Field of Search ..lO2/103; 264/3; 149/5, 6, 7

[5 6] References Cited UNITED STATES PATENTS Kaufman 102/ 103 3,426,528 2/ 1969 Mangum et a1 102/103 3,493,446 2/1970 Braum 102/103 3,108,433 10/1963 De Fries et a1. ..102/103 2,958,288 11/1960 Campbell, Jr. et a1.....l'02/l03 2,995,01 l 8/ 1 961 Kimmel ..264/ 3 3,144,830 8/1964 De Fries et al. 102/103 Primary Examiner-Benjamin A. Borchelt Assistant Examiner-H. .1. Tudor Attorney-R. S. Sciascia, Roy Miller and Gerald F.

Baker [57] ABSTRACT A propellant grain is wrapped with glass fiber tape and fitted with epoxy end pieces to inhibit burning in those areas. A fluorocarbon grain is etched with hydrochloric acid and then immersed in lacquer before being wrapped.

2 Claims, 3 Drawing Figures PAIENTEB OCT 24 I972 BACKGROUND OF THE INVENTION Because previous inhibiting methods for cartridge loaded propellant grains were found to be impractical for fluorocarbon propellant grains, new methods and materials for providing inhibitors were necessarily developed. The old inhibitor materials such as ethyl cellulose and cellulose acetate were found to be inapplicable to fluorocarbon grains because such materials will not bond to the binders used in these grains. The inhibitor means provided by the present invention provides thermal protection to the motor tube and eliminates need for heat barriers and also reduces overall motor costs. The peripheral inhibitor tape further provides structural integrity to the grain under high centrifugal loading.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING:

, FIG. 1 is a side view partly in longitudinal cross section of a propellant grain provided with inhibitors according to the present invention;

FIG. 2 is an end view of the grain in FIG. 1; and FIG. 3 is a detail view.

DETAILED DESCRIPTION OF THE INVENTION:

' As shown in FIG. 1, a propellant grain is fitted with two end inhibitors 12, 14 of epoxy resin or the like the grain is wrapped with inhibiting tape 16. The propellant grain 10 is typical and is shown with a bore 13 and, one one end, a counterbore 20. The other end has an inner tapered portion 22.

Looking at FIG. 2 we see that the illustrated propellant grain is formed with a number of convolutions 17. The number and configuration of convolutions varies with size and design. The simplest design, for example, comprises two orthogonal longitudinal passages.

The fragmentary view in FIG. 3 shows the propellant grain 10 with two wrappings of inhibiting tape 16 and shows the manner of laying up the inhibiting tape with a typical lap joint, for example, of l 1/ l 6 inches.

The propellant grains may be formed by any known process but typically are cast in molds. The grain as it comes from the mold is prepared by covering the ends with tape and then cleansing the remaining surface with soap and cold water. The grain is then dried with a clean wiper, immersed in a 1:1 solution of HCl and etched for 45 minutes.

The etched grains are then rinsed in cool running water, wiped dry and the tape is removed from the ends after which the grains are vacuum dried in an oven at F. A ring of flexible epoxy is next cast in situ on each end of the grain and after each ring is cast the grain is placed in an oven at 200 F. for at least 1 Mi hours to cure the epoxy.

Internal casting fixtures are used in casting the end pieces and these fixtures are left in place for the next operation which consists of three immersions in Viton lacquer insterspersed with half hour drying periods.

Finally the outer surface of the grain is wrapped with tape. The tape is preferably applied using a tape wrapping lathe and is applied in two or more layers. A tape found suitable for this application is a 2-inch wide tape manufactured by Minnesota Mining and Manufacturin Company and designated as Y 9087.

at is c aimed 1s:

1. The process of manufacture of a propellant grain including the steps of:

molding propellant material into a hollow solid having inner and outer substantially cylindrical surfaces; chemically treating said outer surfaces by bathing in a 1:1 solution of HCL; coating said outer surfaces with lacquer; and wrapping said outer surfaces with glass fiber tape. 2. The process of claim 1 wherein said propellant material comprises a fluorocarbon. 

2. The process of claim 1 wherein said propellant material comprises a fluorocarbon. 